With key commands, I almost never take my hand off the mouse. I can do just about any key command with just my left hand and the right hand stays on the mouse. And, with mouse modifiers (shift, ctrl, alt) you obviously still need to have a hand in the mouse. A mouse button, just means you may not need to use your left hand too.
Problem I have is the 4 extra buttons on the side of my mouse (2 each side) are a bit fiddly to use as the mouse is quite small. I like the size of the mouse as I just grip it with the tips of my thumb and fingersand move my fingers, but my wrist stays pretty still. I don’t “palm” the mouse.
I looked at the dimensions of the MX Master and it looks petty huge. I think you would need to “palm” that mouse, which would make using the thumb wheel easy, but maybe not suit my mouse style.